Various types of spirally wound compact filter elements configured for axial flow and housings for these filter elements are known in the art. DE 32 49 151 C2 discloses a compact air filter element comprised of a corrugated filter paper and a flat filter paper. The filter papers are glued together and then wound together to form a filter element of the desired size. Gluing of the filter paper layers is realized by a strip-shaped applied in the edge areas of the filter paper. With this technique the interstices between the corrugated and the flat layers are closed alternatingly at the two end faces so that no direct flow is possible through the channels formed between the filter papers. Air flow, when flowing from the unfiltered air side to the filtered air side, first reaches only branch channel, then passes through the filter paper and flows out from a branch channel on the other side. In comparison to conventional folded filters, these compact air filters have the advantage that for the same size a larger filter surface area is provided or for the same filter surface area a smaller size is made possible.
In folded or pleated filters, servicing of a filter medium is partially done such that the filter insert element is removed from the housing and, by impacting the filter on a hard surface, the dust collected between the folds may be removed so that the service life of the filter insert element can be minimally increased even when only coarse particles are removed and the fine dust that is clogging the pores of the filter medium remain in place. It is also possible that the filter element can be unintentionally damaged should it impact another object while being exchanged. For an example, in case of a compact air filter element wound from paper layers a detachment of the inner adhesive beads may occur. The adhesive beads connect the corrugated layer and the flat cover layer and also close off the channels formed between the layers at the ends. This can result in direct air flow through the channels from the unfiltered side to the filtered side, which is highly undesirable. If this damaged compact air filter element is positioned upstream in an air intake of an internal combustion engine, this can cause severe motor damage.
In addition to detachment of the adhesive layer, impacting the filter element against a hard surface can tear the filter paper in a way that the tear then extends across the adhesive bead. In this case it is also possible that unfiltered air loaded with dirt can pass through the compact air filter element can cause damage.